Bisection of A013697.

Terms

a(0) =1a(1) =12a(2) =57a(3) =245a(4) =1005a(5) =4063a(6) =16327a(7) =65435a(8) =261965a(9) =1048259a(10) =4193742a(11) =16776218a(12) =67107091a(13) =268432305a(14) =1073736223a(15) =4294957340a(16) =17179851485a(17) =68719445272a(18) =274877851009